This invention relates to cranes and, more particularly, to the cable drives for cranes.
The versatility afforded by the use of clam shells is well recognized and they are used with various types of cranes. Some general purpose type cranes are not suited to use with clam shells even though they are equipped with hoist arrangements which could be used to raise and lower a clam shell. In such cranes the cable is both driven off a winch drum (paid-out) and powered back by being recoiled on the drum. In such arrangements the cable is strung along a boom and over idler sheaves to a ball and hook on which the clam shell is supported. One of the problems is that as the clam shell is lowered into engagement with a particular load to be raised, the danger exists that cable will continue to be paid-out even after the downward movement of the clam shell has been interrupted. The weight of the clam shell no longer maintains tension on cable and excess cable paid-out will snarl at the winch drum much in the nature of a snarled line on a fishing reel due to a "backlash". Since heavy duty cable is involved, this snarled condition is extremely difficult to clear.
This invention is concerned with this problem and has as one of its general objects the provision of a cable pay-out and retrieval arrangement which eliminates the possibility of a snarled cable at the winch drum.
Another general object of this invention is to provide a cable drive arrangement which has universal applicability to various types of cranes permitting use of clam shells, and the like, with virtually any type of crane.
A more specific object of this invention is to provide such a cable drive arrangement in association with means for continuously monitoring the load on the cable.